Hi
Friends I got 2 negative reviews in this month without having a fault from my side.

both the cases buyer was satisfied with the designs.
in the first case.
buyer give a positive review and after few days he asked for an extra modification.so I send a $5 min offer to the buyer.but the buyer wants the modification for free.but he accepted the offer and give a negative review saying that I have charged extra money for the modification.

in the second case buyer really like my design and give a positive review.after some days he edited his good review to a bad review and said files are not good quality while downloading.so i download the files from Fiverr and check it.but it looks good in quality.
so i contact Fiverr support about this issue.customer support confirms my files are good quality.so i ask customer support to help the buyer to download good files.they said i want to ask the buyer to contact fiverr support.so i contact buyer.but he is angry with me and said I wasted his money.
I got a negative review because of Fiverr technical issue or buyer computer issue.

as a seller, i like to know who will support me?
their is no value for a designer and his work on fiverr ?

Unfortunately - it’s tough luck, Fiverr does not protect sellers, customer is right, even if the are not.
It’s also a cultural thing, western culture protects buyers, even if they are not right. (and buyers got used to this, and a few of them overdo it and they really behave poorly) Part of doing business. Just like part of doing business in India is bargaining, or gifts in China)

You can do every precaution, like you clearly indicate what is included, how many revisions, etc.

When it’s a modification and it’s not included, you still include it. You can show buyers you are going above and beyond. Factor in this to your original price, if every 10 buyer behaves like this, your price should be 10% higher, that’s it.
Alternatively, you end up using your time as fighting customers, fighting customer support, getting nowhere. Even doing the requested modification for free takes less time, and you will have a happy customer.